Determining the cooling state of a household appliance motor

Abstract

Method for determining a cooling state of a household appliance motor (5) with a winding, in which during a rest state (Mr) of the household appliance motor (5) - resistance values ​​(R1-R3) of the winding are measured at a specified time interval, - at least one resistance difference (ΔR) is determined from the measured resistance values ​​(R1-R3), - which compares at least one resistance difference (ΔR) with a predetermined cooling threshold (Rth) and - the cooling state is determined based on the ratio of the resistance difference (ΔR) to the cooling threshold (Rth).

Description

[0001] The invention relates to a method for determining the cool-down state of a household appliance motor with a single winding, in which the resistance values ​​of the winding are measured. The invention also relates to a household appliance comprising a household appliance motor with a single winding, a control circuit for controlling the household appliance motor, and an evaluation device for determining the cool-down state of the household appliance motor. The invention is particularly advantageously applicable to laundry treatment appliances, especially washing machines, clothes dryers, or combinations thereof.

[0002] A household appliance motor in the form of a brushless DC motor (also known as a "BDLC motor") is known, which is controlled by a motor controller or drive circuit that includes at least one insulated-gate bipolar transistor (IGBT). Methods for determining the cool-down state of such a household appliance motor are known that are based on evaluating a relationship between the temperature of an IGBT and the temperature of a winding. However, such methods are not very reliable. Methods are also known in which a value for the winding temperature is determined by measuring the electrical resistance of this winding. A disadvantage of this method is that manufacturing and material-related tolerances of the resistance are difficult to account for, which generally leads to insufficient accuracy. For example, the cold resistance of the winding is usually not known with sufficient accuracy.

[0003] German patent application DE 101 19 201 A1 discloses a method for determining the cooling state of a household appliance motor with a winding, in which resistance values ​​of the winding are measured at predetermined time intervals during a rest state of the household appliance motor and at least one resistance difference is determined from the measured resistance values.

[0004] DE 37 06 659 C2 discloses a device for determining the winding temperature of a brushless DC motor by determining the ohmic winding resistance of at least one winding, wherein, with the motor running, the determination of the ohmic winding resistance is carried out by a measurement during a period of time in which the winding is in a currentless state.

[0005] DE 10 2013 109 773 A1 discloses a method in which the actual temperature of a motor winding is determined from the winding resistance values ​​without a temperature sensor and, in order to avoid damage to the motor, the current is supplied to the motor taking into account the actual motor temperature.

[0006] The object of the present invention is to overcome at least some of the disadvantages of the prior art and, in particular, to provide a simple and easily implementable method for determining the cooling state of a household appliance motor more accurately and reliably.

[0007] This problem is solved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0008] The problem is solved by a method for determining a cooling state of a household appliance motor with a winding, in which, in particular, during a rest state of the household appliance motor, resistance values ​​of the winding are measured at a predetermined time interval, a resistance difference ΔR is determined from the measured resistance values, the resistance difference ΔR is compared with a predetermined cooling threshold value Rth, and the cooling state is determined based on the ratio of the resistance difference ΔR to the cooling threshold value Rth.

[0009] This method offers the advantage of easily reducing the tolerance chain required to determine the cooling state of a household appliance motor, particularly since the winding temperature does not need to be measured. This, in turn, allows for a more accurate and reliable determination of the cooling state than previously possible. The method can be performed without additional measuring instruments to determine whether the motor has cooled to ambient or room temperature. This reveals whether the motor has recently been operated and preheated. Consequently, the utilization of the household appliance motor can be improved. Furthermore, the installation conditions of the associated household appliance can be better taken into account. In addition, the operating times of drum ball bearings or other components driven by the household appliance motor can be improved, enabling longer operating times in cold conditions.

[0010] The household appliance motor is a component of a household appliance or is intended to be a component of a household appliance.

[0011] A rest state of the household appliance motor can be understood in particular as a state in which the household appliance motor is not operated to achieve a predetermined functionality of the household appliance, or in which a component connected to the household appliance motor does not perform a specific function through its drive.

[0012] A cooling state can be understood, in particular, as a state of the household appliance motor related to a degree of cooling, especially in relation to the ambient temperature of the household appliance motor. It is a further development that the cooling state can assume two possible states, for example, a "cooled down" state and a "not cooled down" state. A cooled down state can correspond, in particular, to a state in which the household appliance motor has cooled down to or is approximately cooled down to an ambient temperature. A not cooled down state can correspond to a state in which the household appliance motor is still undergoing a noticeable cooling process.

[0013] Resistance measurement is performed with a high current to achieve the required resolution. The measurement itself therefore causes the winding to heat up. If measurements are taken repeatedly (at least twice), the resistance measured across the winding increases due to this heating. By adjusting the duration of each measurement or the corresponding current, the number of measurements taken, and the interval between measurements, etc., the temperature gradient ΔT between measurements can be specifically controlled, for example, to enable particularly high accuracy in determining the resistance difference. The current used for a resistance measurement is advantageously so low that a component driven by the household appliance motor does not perform any function of the appliance during the measurement, e.g., the drum of a washing machine or dryer does not rotate.

[0014] A resistance value can be understood in particular as a value of electrical resistance, for example an ohmic resistance.

[0015] The resistance difference ΔR can be sign-sensitive or an absolute value. For example, if the resistance difference ΔR corresponds to a difference between exactly two resistance values ​​R1 and R2, then ΔR = R2 - R1 or ΔR = |R2 - R1| can hold true. In general, a resistance value Ri can be understood as a resistance value measured at a time ti, i.e., Ri = R(t = ti).

[0016] The household appliance motor can have one or more windings. The procedure can be carried out using one or more windings.

[0017] A size ratio can be understood as the result of a numerical size comparison, for example by applying the mathematical operators "greater than" or ">", "greater than or equal to" or ">=", equal to or "=", "less than or equal to" or "<=" or "less than" or "<".

[0018] One embodiment of the method dictates that a sufficiently cooled state is determined when the resistance difference ΔR is at least greater than the cooling threshold Rth, i.e., greater than or equal to the cooling threshold Rth. In other words, the cooled state is assumed to exist when ΔR > Rth or when ΔR ≥ Rth. This offers the advantage that the cooled state can be determined particularly easily and reliably. This method exploits the fact that the time gradient of the winding temperature is small in the cooled state because the winding has already cooled down. If the resistance of the winding is measured in the cooled state, the winding temperature rises comparatively sharply compared to the winding temperature immediately before the measurement, so that the electrical resistance of the winding also changes relatively sharply between two measurements.Therefore, the corresponding resistance difference ΔR is also large.

[0019] Another design involves applying standalone pulses to the winding to measure resistance values. Between pulses, the winding is not energized (Iw = 0). The pulses can be identical, for example, in terms of current intensity, pulse duration, etc. This allows for a particularly simple and precise resistance measurement.

[0020] In another variation, current pulses are applied to the winding in addition to a continuous (non-interrupted or non-pulsed) current to measure the resistance values. Between the pulses, the winding is energized (Iw > 0). The continuous current can be constant. The pulses can be identical, for example, with respect to their current intensity, pulse duration, etc. In other words, pulsed current can be superimposed on a continuous current. This offers the advantage of allowing for more versatile control over the heating of the windings by the current. Another advantage is that this method holds the motor rotor in place, thus eliminating the typical jerk when aligning the rotor during startup.

[0021] Another embodiment involves applying a continuous electric current to the winding to measure the resistance values, particularly with a current of constant magnitude. This advantageously provides yet another way to influence the heating of the windings through the current application.

[0022] Furthermore, it is a possible configuration that the household appliance motor is a brushless direct current motor (BLDC motor).

[0023] It is also possible to configure the system in which the brushless DC motor or its windings are controlled by means of at least one semiconductor switch, and the cooling state is additionally determined based on the temperature of at least one semiconductor switch. This allows for an even more reliable determination of the cooling state, since the temperature of the semiconductor switch can be used to validate the cooling state determined by the method described above. This configuration assumes that the heat capacity of a control circuit or power module is generally significantly smaller than the heat capacity of the motor, and that when the ambient temperature has been reached at the motor (and consequently also at the winding), the ambient temperature will also be reached at the semiconductor switch.For example, a cooling state of the winding determined by the above method can be positively confirmed by a sufficiently cold semiconductor switch and / or called into question or rejected by a sufficiently warm semiconductor switch. A temperature sensor on the semiconductor switch can be used for this purpose.

[0024] The at least one semiconductor switch can be a component of a drive circuit or motor controller for the BLDC motor. This at least one semiconductor switch can be, for example, an IGBT or a MOSFET. The drive circuit can be a component of the BLDC motor itself or a separate but electrically connected component.

[0025] It is also possible to determine the resistance difference ΔR from at least two consecutively measured resistance values. More than two resistance values ​​may have been measured beforehand. This configuration offers the advantage of a particularly simple determination of the resistance difference ΔR.

[0026] For example, if four resistance values ​​R1 to R4 are measured, several resistance differences ΔR can be determined according to ΔR = R1 - R2, ΔR = R2 - R3, and ΔR = R3 - R4 (or a corresponding absolute value). A further development is to determine the resistance difference ΔR from two resistance values ​​measured in immediate succession.

[0027] Furthermore, one embodiment involves measuring at least two resistance values ​​from a first group with the same initial time interval, measuring at least two resistance values ​​from a second group with the same second time interval, and having a third time interval between the groups that is greater than both the initial and second time intervals. This achieves the advantage that resistance differences ΔR can be determined over a longer period, thus minimizing the impact on the winding's cooling behavior after motor operation. A further development involves making the initial and second time intervals equal. This embodiment offers the advantage of allowing the winding to cool down between multiple resistance difference measurements. A group can also be configured to have exactly two resistance values.

[0028] Another feature is that different actions are performed depending on whether the device is in a cool-down state or not. For example, a decision can be made as to whether the household appliance motor is operated to perform a function of the associated appliance, or not (yet).

[0029] The task can also be accomplished by a household appliance designed to perform the procedure as described above. The household appliance can be designed analogously to the procedure and offers the same advantages.

[0030] One embodiment of the household appliance comprises a household appliance motor with one winding, a control circuit for the household appliance motor, and an evaluation unit for determining when the household appliance motor has cooled down, the evaluation unit being configured to perform the procedure as described above. The control circuit can be part of the household appliance motor.

[0031] One embodiment of the appliance is a laundry treatment device. This laundry treatment device can be a washing machine, a tumble dryer, or a combination thereof (washer-dryer). Specifically, if the laundry treatment device is a washing machine or a washer-dryer, the method can be used to determine whether the motor has recently been operated and preheated, and then to adjust spin profiles to the temperature of a drum ball bearing.

[0032] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following schematic description of an exemplary embodiment, which will be explained in more detail in conjunction with the drawings. Fig. Figure 1 shows a sectional view of a household appliance according to the invention; Fig. Figure 2 shows a plot of temperature against time for a temperature profile of a winding of the household appliance motor and a temperature profile of a semiconductor switch of a control circuit of the household appliance motor; Fig. Figure 3 shows a plot of a current impressed into a winding, a temperature of the winding and an electrical resistance of the winding against time for three resistance measurements according to a first embodiment; Fig. 4 shows one to Fig. 3 analog plots for three resistance measurements according to a second embodiment; Fig. 5 shows one to Fig. 3. Analog plotting for three resistance measurements according to a third embodiment; and Fig. Figure 6 shows a plot of current against time for several resistance measurements according to another embodiment.

[0033] Fig. Figure 1 shows a sectional view of a household appliance according to the invention in the form of a washing machine 1, optionally with a drying function (washer-dryer). The washing machine 1 has a drum 2 for receiving laundry to be washed and / or dried through a loading opening that can be closed by a front door 3. The drum 2 is rotatably mounted horizontally via at least one drum ball bearing (not shown). For its rotation, the drum 2 is connected via a drive shaft 4 to a household appliance motor in the form of a BLDC motor 5, which serves as the drive motor. The BLDC motor 5 may have a control circuit 6 or be connected to the control circuit 6. The control circuit 6 is connected to a central control circuit 7, which can also serve as an evaluation unit, in particular for determining whether the BLDC motor 5 has cooled down.

[0034] For this purpose, resistance values ​​R1, R2, R3 are measured at predetermined time intervals during a rest state of the BLDC motor 5 (see Fig. 3 to Fig. 6) of a winding (not shown) of the BLDC motor 5 is measured. Then, using the control circuit 7, resistance differences ΔR are determined from the measured resistance values ​​R1, R2, R3. Each resistance difference ΔR is compared with a predetermined cooling threshold value Rth using the control circuit 7, and based on the ratio of the resistance difference to the cooling threshold value, a cooling state of the BLDC motor 5 is determined.

[0035] Fig. Figure 2 shows a plot of temperature T in °C against time t in h for a temperature Tw curve of a winding of the BLDC motor 5 and a temperature TIGBT curve of a semiconductor switch of the control circuit 6 in the form of an IGBT (not shown).

[0036] At the beginning of the time period shown, between t = 0 and approximately t = 15 minutes, the BLDC motor 5 is operated. As a result, the temperatures Tw and TIGBT rise sharply from room temperature (here approximately 22 °C) to approximately 85 °C and approximately 80 °C, respectively. At approximately t = 15 minutes, the BLDC motor 5 is switched off and enters a standby state Mr. In this standby state Mr., the winding and the TIGBT cool down.

[0037] The corresponding cooling profile of the winding temperature Tw in the idle state Mr exhibits a characteristic shape that follows an exponential function. A corresponding time constant results from the thermal properties of the BLDC motor 5. In any case, the cooling profile becomes steadily flatter with increasing time t and, after a finite time, stabilizes at the ambient temperature with sufficient accuracy. In the idle state Mr, three cooling phases can be distinguished: a first cooling phase I immediately following the switching off of the BLDC motor 5, in which a high temperature gradient ΔTI occurs; a "steady state" III corresponding to a cooled state, in which a very low temperature gradient ΔTIII occurs (which can even become practically zero); and an intermediate phase II with a temperature gradient ΔTII where ΔTI > ΔTII > ΔTIII.

[0038] When the electrical resistance values ​​R1, R2, R3 of the winding are measured in the region of the high temperature gradient ΔTI, the high electric current impressed into the winding during the measurement does not lead to a heating or temperature increase ΔTw of the winding to the same extent as in a comparable measurement in or near steady-state phase III. This is because, in the cooling phase I, a temperature increase ΔTw of the winding generated by the resistance measurement can be dampened, completely eliminated, or even overcompensated by the strong natural cooling, especially if |ΔTI| >> |ΔTw|. Consequently, a resistance difference ΔR = R2 - R1 is rather small in the cooling phase I and can even become negative.

[0039] In steady-state phase III, natural cooling plays no role or no noticeable role, so the high electric current impressed into the winding during the measurement leads to a significant temperature increase ΔTw of the winding. The resistance difference ΔR is therefore significantly larger for steady-state phase III than for cooling phase I or intermediate phase II.

[0040] To determine the cooled state of the winding, a limit value Rth of the resistance difference ΔR is defined, corresponding to a state of the winding in or near the steady state. If the defined resistance difference ΔR reaches and / or exceeds the limit value Rth, i.e., ΔR > Rth or ΔR >= Rth, a cooled state is assumed.

[0041] The temperature TIGBT of the semiconductor switch also decreases steadily in the idle state Mr, and faster than the temperature Tw, possibly according to an exponential function.

[0042] Fig. Figure 3 shows a plot of a current Iw impressed into a winding, a temperature ϑ of the winding and an electrical resistance R of the winding against time t for three resistance measurements according to a first embodiment.

[0043] To measure the resistances R1, R2 and R3, isolated rectangular current pulses P1, P2 and P3 of the same amplitude and duration Δt1, Δt2 and Δt3 respectively are impressed into the winding at equal intervals.

[0044] Before the first current pulse P1 is applied, the winding temperature Tw is constant, for example, because it is in a cooled state. During the duration Δt1 of the first current pulse P1, the temperature Tw rises and then falls again between the two current pulses P1 and P2, but not sufficiently to reach the temperature Tw that was present before the first current pulse P1 when the second current pulse P2 is applied. During the duration Δt2 of the second current pulse P1, the temperature Tw rises again and then falls again between the two current pulses P2 and P3, but not sufficiently to reach the temperature Tw that was present before the second current pulse P2 when the third current pulse P3 is applied. During the duration Δt3 of the third current pulse P1, the temperature Tw rises again and then falls again after the third current pulse P3.

[0045] The resistance values ​​R1, R2, and R3 corresponding to the current pulses P1, P2, and P3 are measured at the end of or shortly after the durations Δt1, Δt2, and Δt3, respectively, when the associated temperature increases are at their highest. Differences between successive resistance values ​​R1, R2 and R2, R3 correspond to differences ΔTw in the temperatures Tw at these times, where R1 < R2 < R3.

[0046] At least one resistance difference ΔR = R2-R1, R3-R2, and / or R3-R1 can be compared to a threshold value Rth (e.g., by checking if ΔR > Rth) to determine whether the winding is in a cooled state. A further development is the use of a numerical or logical combination of several resistance differences ΔR to determine whether the winding is in a cooled state.

[0047] These considerations can also be carried out for only two resistance measurements R1 and R2 or for more than three resistance measurements.

[0048] Fig. 4 shows one to Fig. 3. Analog plot for three measurements of resistances R1 to R3 according to a second embodiment. Here, the current pulses P1, P2, and P3 are generated in addition to a continuous, constant current Ik in the winding. Therefore, the total current impressed into the winding is Iw = Ik + P1 + P2 + P3.

[0049] Fig. 5 shows one to Fig. 3. Analogous plot for three resistance measurements according to a third embodiment, in which the winding for measuring the resistance values ​​R1 to R3 is energized with a current Ik of constant magnitude. Therefore, the total current impressed into the winding is Iw = Ik.

[0050] Fig. Figure 6 shows a plot of a current Iw impressed into the winding against time t for several resistance measurements – for example, according to the Fig. 3 to 5, however analogous to Fig. 3 shown - as part of yet another embodiment.

[0051] For each of the current pulses P1, P2, P3, a corresponding resistance value R1, R2, or R3 is measured. The measurements are performed in groups, with the same current pulses P1, P2, P3 being applied to each of the groups G1 to G4, and consequently, the resistance values ​​R1, R2, or R3 being measured identically. The resistance values ​​R1 to R3 of the groups G1 to G4 are measured with equal time intervals, which are shorter than the time intervals between the groups G1 to G4. Reference symbol list 1 washing machine 2 washing drums 3 Door 4 drive shaft 5 BLDC motor 6 Control circuit 7 Central control circuit G1 - G4 Group I Cooling phase II Intermediate Phase III. Inertia Phase Ik Constant electric current impressed into a winding Iw Electric current impressed into a winding P1 - P3 Current pulse impressed into a winding R1 - R3 resistance values BLDC motor idle state R resistance of the winding Rth cooling threshold Temperature t time Temperature of a winding TIGBT temperature of a semiconductor switch ΔR resistance difference ΔTm temperature increase of the winding ΔTw Temperature increase of the winding ΔTI Temperature gradient during the cooling phase ΔTII Temperature gradient in the intermediate phase ΔTIII temperature gradient in the steady-state phase Δt1 - Δt3 Duration of the current pulses ϑ Temperature of the winding

Claims

[1] Method for determining a cooling state of a household appliance motor (5) with a winding, in which during a rest state (Mr) of the household appliance motor (5) - resistance values ​​(R1-R3) of the winding are measured at a specified time interval, - at least one resistance difference (ΔR) is determined from the measured resistance values ​​(R1-R3), - which compares at least one resistance difference (ΔR) with a predetermined cooling threshold (Rth) and - the cooling state is determined based on the ratio of the resistance difference (ΔR) to the cooling threshold (Rth). [2] Method according to claim 1, wherein a cooled state is detected when the resistance difference (ΔR) is at least greater than the cooling threshold (Rth). [3] Method according to one of the preceding claims, wherein standalone pulses (P1-P3) are impressed into the winding to measure the resistance values ​​(R1-R3). [4] Method according to one of claims 1 or 2, wherein current pulses (P1-P3) are impressed into the winding in addition to a continuous current (Ik) to measure the resistance values ​​(R1-R3). [5] Method according to one of claims 1 or 2, wherein a continuous current (Ik) of constant strength is impressed into the winding to measure the resistance values ​​(R1-R3). [6] Method according to any of the preceding claims, wherein the household appliance motor (5) is a brushless DC motor. [7] Method according to one of the preceding claims, wherein the brushless DC motor (5) is controlled by means of at least one semiconductor switch and the cooling state is additionally determined based on a temperature (TIGBT) of at least one semiconductor switch. [8] Method according to any of the preceding claims, wherein more than two resistance values ​​(R1-R3) are measured and the resistance difference (ΔR) is determined from at least two consecutively measured resistance values ​​(R1, R2; R2, R3; R1, R3). [9] Method according to any of the preceding claims, wherein at least two resistance values ​​(R1-R3) of a first group (G1-G3) are measured with the same first time interval, at least two resistance values ​​(R1-R3) of a second group (G2-G4) are measured with the same second time interval, and a third time interval between the groups (G1-G4) is greater than the first time interval and than the second time interval. [10] Method according to any of the preceding claims, wherein different actions are performed depending on whether the cooling state is present or not. [11] Household appliance (1) comprising a household appliance motor (5) with a winding, a control circuit (6) for controlling the household appliance motor (5) and an evaluation device (7) for determining a cooling state of the household appliance motor (5), wherein the evaluation device (7) is configured to carry out the method according to one of the preceding claims. [12] Household appliance (1) according to claim 11, wherein the household appliance (1) is a laundry treatment appliance.

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